Normal serum provides a sufficient quantity of endogenous proteins to saturate and block non-specific binding sites on fixed samples or assayed substrates. Normal goat serum is used extensively for the blocking of non-specific antibody binding in immunohistochemistry staining, and in other applications of antibodies. The goat serum blocks the binding of Fc receptors in the sample to the primary and secondary antibodies used in the experiment. It also blocks the non-specific binding of the antibodies to the sample. Often the blocking serum is from the species in which the secondary antibodies were raised. Normal goat serum may be used as a blocking agent or negative control in immunoassays. For immunohistochemistry and immunocytochemistry, goat serum is used between 1%-20% as a blocking agent in various studies.